Proposals have been made heretofore for a vertically disposed screw connected to the cab by a nut mating with the screw. All are subject to serious defects and shortcomings. In some designs the screw is rotated by stationary power means mounted at one end of the screw and, in others, the screw remains stationary and a motor mounted on the cab rotates the nut. Examples of such elevators are disclosed in Schnitzer U.S. Pat. No. 1,161,255, Brown U.S. Pat. No. 2,004,060, Brubaker U.S. Pat. No. 2,627,321, Kinsman U.S. Pat. No. 2,857,021, Katz U.S. Pat. No. 3,799,292, MacChesney U.S. Pat. No. 3,215,227, Letz U.S. Pat. No. 3,468,401, Todd U.S. Pat. No. 2,527,897 and Grove U.S. Pat. No. 3,802,290. Such systems have very restricted performance capabilities and lack reliable safeguards against mishaps, flexible control systems, provision for operating the cab at different speeds, safeguards against operating the elevator unless all doors are locked closed, and provision for propelling the cab with pressurized fluid.